From what we understand Ishida weighed in at 92KG, or just shy of 203lbs, which is above the lower limit of the Heavyweight. The JBC had set Ishida a minimum target of 90.7KG, just less than 200lbs, and it seems likely that if he had failed to come in above that lower weight they'd have refused to sanction the contest. Thankfully Ishida did the weight with plenty to spare.
Although Ishida had made his name fighting at 154lbs or 69.85KG's he has bulked up really well and and has looked very good in recent training pictures.
Talking about his training Ishida has been sparring some top fighters including WBA Cruiserweght champion Denis Lebedev to help him prepare for the strength and power of Fujimoto. We've not been informed of all of Ishida's sparring partners be we've been lead to believe that many of them are Cruiserweights which would match the relative size of Fujimoto who is a small thick built Heavyweight himself.
(Image courtesy of boxingnews.jp, video courtesy of TUGmanBOX)